1. Technical Field of the Invention
The invention relates generally to memory storage devices; and, more particularly, it relates to dibit extraction being performed within such memory storage devices.
2. Description of Related Art
As is known, many varieties of disk drives, such as magnetic disk drives are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
Within such disk drives, there is a need to characterize the channel that is employed to read/write information to the memory storage device that is employed to store/retrieve data to/from the media. One term sometimes used in the art when characterizing this channel response is dibit extraction. The extracted signal dibit is used to find the signal characteristics of the channel, and the noise dibit is used to find the noise characteristics of the channel. In the art, there are different ways to perform dibit extraction.
Many prior art approaches to dibit extraction, particularly the practical, real-time implementations, are not well suited to accommodate the newer technology of perpendicular magnetic recording (PMR), or the increasingly popular noise dibit. Practical implementations in the prior art use approximations that lead to scaling and DC boost problems. The incorrect scaling can be corrected relatively easily (even ignored in many cases), but the DC boost cannot.
The previous technology of longitudinal magnetic recording (LMR) did not exhibit the DC boost problem in signal dibit extraction because the LMR channel is DC free and the signal dibit is DC free, so the DC boost was zeroed out. However, signal dibits in PMR channels are not DC free, and noise dibits in both PMR and LMR channels are not DC free. Therefore, the DC boost problem can no longer be ignored.
Generally speaking, dibit extraction based on a periodic, maximal length, PN (pseudo-random noise) sequence is a highly flexible tool that can be used to identify many of the signal, noise, and nonlinear characteristics of a magnetic read/write channel. For more details, the reader is directed to the References listed below. There is seemingly a continual need in the art to find and develop better means by which dibit extraction can be performed.